OBJECTIVE: To determine the precise timing of developmental events during primate preimplantation embryogenesis and assess the relationship between the timing of cleavage events and developmental potential in vitro. RESULTS Using time-lapse videoicrogaphy, we have determined the precise timing of syngamy, early cleavage-stage divisions, compaction, blastocele formation and zona escape during preimplantation development of macaque embryos in vitro, and demonstrated that precise timing of specific early cleavage-stage events can be used as a noninvasive indicator of developmental potential in vitro. FUTURE DIRECTIONS We plan to use time-lapse videomicrography to compare the timing of development in embryos derived from in vitro versus in vivo matured oocytes, and to determine the precise timing of developmental events during human preimplantation embryo development in vitro. KEY WORDS embryo, macaque, cinematography, in vitro fertilization